Cell wall xyloglucan epitope modifications during flooding-induced root aerenchyma development in select cool-season legumes

Characterizing the extracellular mechanisms plants use to adapt to water immersion could provide avenues for crop improvement in the face of periodic flooding. One such mechanism is hypoxia-induced aerenchyma formation. The formation of lysigenous aerenchyma occurs through programmed cell death (PCD) that may require the chemical modification of select polysaccharides in root cell walls. Currently, the precise mechanism of cell wall structural modification is not fully defined. To better characterize this mechanism, we investigated whether a relationship exists between modification of cell wall xyloglucans through removal of fucosyl functional groups and the formation of root aerenchyma in agriculturally relevant Fabaceae species. Characterization was conducted through the immunolabeling of specific xyloglucan epitopes within root cell walls during a 48-hour flooding time series. Immunolabeling results suggest progressive alterations in the accessibility or abundance of fucosylated and non-fucosylated xyloglucan epitopes in cell walls bordering developing aerenchyma cavities during PCD. Additionally, we performed an enzymatic pretreatment to remove select cell wall polymers prior to immunolabeling for xyloglucan, xylan and crystalline cellulose. These pretreatments demonstrate potential in vitro epitope masking constraints in root cell walls near developing aerenchyma. Our findings suggest that chemical modification to xyloglucans occurs in tandem with modification of select cell wall pectin epitopes. Our results elucidate previously uncharacterized cell wall carbohydrate remodeling during PCD leading to aerenchyma formation among legume species.